Method and apparatus for trimming an internal combustion engine

ABSTRACT

A fuel injection control system and method for trimming an internal combustion engine during a fuel injection event based upon engine operating conditions, the control system including an electronic controller in electrical communication with the engine, the controller being operable to detect the operating mode of each injector of the engine and alter each injector operating mode as desired.

TECHNICAL FIELD

This invention relates generally to electronically controlled fuelinjection systems and, more particularly, to a method and apparatus fordetermining a desired duration at which to set a delay during multipleshot fuel injections for each injector device of the injection system.

BACKGROUND ART

Electronically controlled fuel injectors are well known in the artincluding hydraulically actuated and mechanically actuatedelectronically controlled fuel injectors. An electronically controlledfuel injector typically injects fuel into a specific engine cylinder asa function of an injection signal received from an electroniccontroller. These signals include waveforms that are indicative of adesired injection rate as well as the desired timing and quantity offuel to be injected into the cylinders.

Emission regulations pertaining to engine exhaust emissions areincreasingly becoming more restrictive throughout the world including,for example, restrictions on the emission of hydrocarbons, carbonmonoxide, particulate and nitrogen oxides (NO_(x)). Tailoring the numberand the parameters of the injection fuel shots during a particularinjection event are ways in which to control emissions and meet suchemission standards. As a result, techniques for generating split ormultiple fuel injections during an injection event have been utilized tomodify the burn characteristics of the combustion process in an attemptto reduce emissions and noise levels. Generating multiple injectionsduring an injection event typically involves splitting the total fueldelivery to the cylinder during a particular injection event into two ormore separate fuel injections, generally referred to as a pilotinjection fuel shot, a main injection fuel shot and/or an anchorinjection fuel shot. As used throughout this disclosure, an injectionevent is defined as the injections that occur in a cylinder during onecycle of the engine. For example, one cycle of a four cycle engine for aparticular cylinder, includes an intake, compression, expansion, andexhaust stroke. Therefore, the injection event in a four stroke engineincludes the number of injections, or shots, that occur in a cylinderduring the four strokes of the piston. The term shot as used in the artmay also refer to the actual fuel injection or to the command currentsignal to a fuel injector or other fuel actuation device indicative ofan injection or delivery of fuel to the engine. At different engineoperating conditions, it may be necessary to use different injectionstrategies in order to achieve both desired engine operation andemissions control.

In the past, the controllability of split or multiple injections hasbeen somewhat restricted by mechanical and other limitations associatedwith the particular types of fuel injectors utilized. For example, whendelivering a split or multiple injection current waveform to a pluralityof fuel injectors, some injectors will actually deliver the split fueldelivery to the particular cylinder whereas some injectors will delivera boot fuel delivery. A boot type of fuel delivery generates a differentquantity of fuel as compared to a split type fuel delivery since in aboot type delivery, the fuel injection flow rate never goes to zerobetween the respective fuel shots. Conversely, in a split fuel delivery,the fuel injection flow rate does go to zero between the respective fuelshots. As a result, more fuel is delivered in a boot type delivery ascompared to a split fuel delivery. Even with more advancedelectronically controlled injectors, during certain engine operatingconditions it is still sometimes difficult to accurately control fueldelivery.

When dealing with split or multiple fuel injection and the generaleffects of a boot type fuel delivery and the fuel injection rate shapingwhich results therefrom, desired engine performance is not alwaysachieved at all engine speeds and engine load conditions. Based uponoperating conditions, the injection timing, fuel flow rate and injectedfuel volume are desirably optimized in order to achieve minimumemissions and optimum fuel consumption. This is not always achieved in amultiple injection system due to a variety of reasons includinglimitations on the different types of achievable injection ratewaveforms and the timing of the fuel injections occurring during theinjection events. As a result, problems such as injecting fuel at a rateor time other than desired within a given injection event and/orallowing fuel to be injected beyond a desired stopping point canadversely affect emission outputs and fuel economy. From an emissionsstandpoint, either a split or boot fuel delivery may be preferable,depending on the engine operating conditions.

In a system in which multiple injections and different injectionwaveforms are achievable, it is desirable to control and deliver anynumber of separate fuel injections to a particular cylinder so as tominimize emissions and fuel consumption based upon the operatingconditions of the engine at that particular point in time. This mayinclude splitting the fuel injection into more than two separate fuelshots during a particular injection event and/or adjusting the timingbetween the various multiple fuel injection shots in order to achievethe desired injector performance, that is, a split or a boot type fueldelivery, based upon the current operating conditions of the engine.

Accordingly, the present invention is directed to overcoming one or moreof the problems as set forth above.

DISCLOSURE OF THE INVENTION

In one aspect of the present invention, there is disclosed anelectronically controlled fuel injection system which is capable ofdelivering multiple fuel injections to a particular cylinder of aninternal combustion engine during a single injection event. The presentsystem includes means for variably determining whether two, three, ormore separate fuel injections or fuel shots are desired during a fuelinjection event at given engine operating conditions including enginespeed and engine load. In this regard, in a preferred embodiment, fuelis apportioned between a first or pilot shot, a second or main shot anda third or anchor shot, each separate fuel injection shot beingdelivered when the cylinder piston is located within a predeterminedrange during a particular piston stroke. The present system alsoincludes means for varying the timing and fuel quantity associated withthe main shot, the timing and the fuel quantity associated with theanchor shot, as well as the duration of the anchor delay, based upon theoperating conditions of the engine.

Under certain operating conditions, the proximity of the main and anchorshots and the resultant internal injector hydraulics and/or mechanicsleads to a rate shaping effect of the third or anchor injection. As aresult, although the first or pilot injection, when used, is typically adistinct injection as compared to the second, or main, and the third, oranchor, injections, a distinct anchor injection is not always apparent.The present invention enables determination as to whether a giveninjector is delivering a distinct third shot and, based uponconsiderations such as engine performance, minimization of emissions,injector durability and so forth, the present system alters the anchorshot delay, if necessary, to achieve the desired injector performance.

These and other aspects and advantages of the present invention willbecome apparent upon reading the detailed description in connection withthe drawings and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, references may bemade to the accompanying drawings in which:

FIG. 1 is a schematic view of an electronically controlled injector fuelsystem used in connection with one embodiment of the present invention;

FIG. 2 is an exemplary schematic illustration of a current waveformsequentially aligned with a corresponding fuel injection rate trace;

FIG. 3 is a schematic profile illustrating how the volume of fuelinjected varies according to the duration of the anchor delay;

FIG. 4a is a first segment of a logic diagram showing the operation ofthe present invention; and

FIG. 4b is a second segment of a logic diagram showing the operation ofthe present invention.

BEST MODE CARRYING OUT THE INVENTION

Referring to FIG. 1, there is shown one embodiment of a hydraulicallyactuated electronically controlled fuel injection system 10 in anexemplary configuration as adapted for a direct-injection compressionignition engine 12. Fuel system 10 includes one or more electronicallycontrolled fuel injectors 14 which are adapted to be positioned in arespective cylinder head bore of the engine 12. While the embodiment ofFIG. 1 applies to an in-line six cylinder engine, it is recognized andanticipated, and it is to be understood, that the present invention isalso equally applicable to other types of engines such as V-type enginesand rotary engines, and that the engine may contain any plurality ofcylinders or combustion chambers.

The fuel system 10 of FIG. 1 includes an apparatus or means 16 forsupplying actuation fluid to each injector 14, an apparatus or means 18for supplying fuel to each injector, electronic control means 20 forcontrolling the fuel injection system including the manner and frequencyin which fuel is injected by the injectors 14 including timing, numberof injections per injection event, fuel quantity per injection, timedelay between each injection, and the injection profile. The system mayalso include apparatus or means 22 for recirculating fluid and/orrecovering hydraulic energy from the actuation fluid leaving eachinjector 14.

The actuating fluid supply means 16 preferably includes an actuatingfluid sump or reservoir 24, a relatively low pressure actuating fluidtransfer pump 26, an actuating fluid cooler 28, one or more actuatingfluid filters 30, a high pressure pump 32 for generating relatively highpressure in the actuation fluid, and at least one relatively highpressure actuation fluid manifold or rail 36. A common rail passage 38is arranged in fluid communication with the outlet from the relativelyhigh-pressure actuation fluid pump 32. A rail branch passage 40 connectsthe actuation fluid-inlet of each injector 14 to the high-pressurecommon rail passage 38.

The apparatus 22 may include a waste accumulating fluid control valve 50for each injector, a common recirculation line 52, and a hydraulic motor54 connected between the actuating fluid pump 32 and recirculation line52. Actuation fluid leaving an actuation fluid drain of each injector 14would enter the recirculation line 52 that carries such fluid to thehydraulic energy recirculating or recovering means 22. A portion of therecirculated actuation fluid is channeled to high-pressure actuationfluid pump 32 and another portion is returned to actuation fluid sump 24via recirculation line 34.

In a preferred embodiment, the actuation fluid is engine lubricating oiland the actuating fluid sump 24 is an engine lubrication oil sump. Thisallows the fuel injection system to be connected as a parasiticsubsystem to the engine's lubricating oil circulation system.Alternatively, the actuating fluid could be fuel.

The fuel supply means 18 preferably includes a fuel tank 42, a fuelsupply passage 44 arranged in fluid communication between the fuel tank42 and the fuel inlet of each injector 14, a relatively low pressurefuel transfer pump 46, one or more fuel filters 48, a fuel supplyregulating valve 49, and a fuel circulation and return passage 47arranged in fluid communication between each injector 14 and fuel tank42.

Electronic control means 20 preferably includes an electronic controlmodule (ECM) 56, also referred to as a controller, the use of which iswell known in the art. ECM 56 typically includes processing means suchas a microcontroller or microprocessor, a governor such as aproportional integral derivative (PID) controller for regulating enginespeed, and circuitry including input/output circuitry, power supplycircuitry, signal conditioning circuitry, solenoid driver circuitry,analog circuits and/or programmed logic arrays as well as associatedmemory. The memory is connected to the microcontroller or microprocessorand stores instruction sets, maps, lookup tables, variables, and more.ECM 56 may be used to control many aspects of fuel injection including(1) the fuel injection timing, (2) the total fuel injection quantityduring an injection event, (3) the fuel injection pressure, (4) thenumber of separate injections or fuel shots during each injection event,(5) the time intervals between the separate injections or fuel shots,(6) the time duration of each injection or fuel shot, (7) the fuelquantity associated with each injection or fuel shot, (8) the actuationfluid pressure, (9) current level of the injector waveform, and (10) anycombination of the above parameters. Each of such parameters may bevariably controllable independent of engine speed and load. ECM 56receives a plurality of sensor input signals S₁-S₈ which correspond toknown sensor inputs such as engine operating conditions including enginespeed, engine temperature, pressure of the actuation fluid, cylinderpiston position and so forth that may be used to determine the precisecombination of injection parameters for a subsequent injection event.

For example, an engine temperature sensor 58 is illustrated in FIG. 1connected to engine 12. In one embodiment, the engine temperature sensorincludes an engine oil temperature sensor. However, an engine coolanttemperature sensor can also be used to detect the engine temperature.The engine temperature sensor 58 produces a signal designated by S₁ inFIG. 1 and is input to ECM 56 over line S₁. In the particular exampleillustrated in FIG. 1, ECM 56 issues control signal S₉ to control theactuation fluid pressure from pump 32 and a fuel injection signal S₁₀ toenergize a solenoid or other electrical actuating device within eachfuel injector thereby controlling fuel control valves within eachinjector 14 and causing fuel to be injected into each correspondingengine cylinder. Each of the injection parameters are variablycontrollable, independent of engine speed and load. In the case of fuelinjectors 14, control signal S₁₀ is a fuel injection signal that is anECM commanded current to the injector solenoid or other electricalactuator.

It is recognized that the type of fuel injection desired during anyparticular fuel injection event will typically vary depending uponvarious engine operating conditions. In an effort to improve emissions,it has been found that delivering multiple fuel injections to aparticular cylinder during a fuel injection event at certain engineoperating conditions achieves both desired engine operation as well asemissions control.

FIG. 2 shows an exemplary current wave trace or waveform 60 having apilot current pulse 62, a main current pulse 64, and an anchor currentpulse 66 sequentially aligned with a rate trace profile 68 illustratingthe fuel injection flow rate. The rate trace profile 68 includes a pilotshot 70 responsive to the pilot pulse 62, a main shot 72 responsive tothe main pulse 64 and an anchor shot 74 responsive to the anchor pulse66.

An anchor delay current signal 76, separating the main and anchor pulsesignals 64 and 66, produces a corresponding anchor delay 78 when themain and anchor shots 72 and 74 operate in a split condition, i.e., thefuel flow rate is significantly reduced for the duration of the anchordelay current signal as illustrated by the split profile segment 80shown in FIG. 2. In one embodiment, for an injection signal utilizingtwo injections, the injections may be referred to generically as being afirst injection, e.g., main injection, a second injection, e.g., ananchor injection, and an injection delay, e.g., an anchor delay.

Due to the fact that it is difficult to produce cylinder injectionsystems having identical operating characteristics, and because the mainand anchor shots 72 and 74 occur close together, it is possible that theduration of the anchor delay current signal 76 will be insufficient toproduce a split between the main and anchor shots 72 and 74, i.e., asignificant reduction in the fuel flow rate is not realized. Thisoccurrence is known as a boot condition and is illustrated by the bootprofile segment 82 shown in FIG. 2.

Depending on variables such as ambient operating conditions, desiredengine performance, minimized emissions and so forth, it may beadvantageous, in certain scenarios, for the injectors to function in asplit mode. In other situations, it may be advantageous for theinjectors to function in a boot condition. Whichever mode is preferred,preferably all of the injectors function in the desired mode. To achievethe desired mode, the split/boot operating condition of each injector isdetected. Thereupon, injectors found to be operating in the undesiredcondition are corrected to function in the desired mode.

In one embodiment, the operating mode of an injector can be determinedby monitoring changes in the volume of fuel desired by the governor whenthe engine is in a steady state condition. FIG. 3 illustrates thedifference in the volume of fuel delivered by a fuel injector for thesame injection command if operating in a split mode, as compared to aboot mode for a given rail pressure and main pulse signal 64 duration.Generally, as described elsewhere herein, the duration of the anchordelay affects the operating mode of the injector, e.g. whether itdelivers fuel in a spilt mode or a boot mode. As shown in FIG. 3, foranchor durations less than ΔX, the curve profile 82′ indicates that theinjector is operating in a boot mode. The curve profile 80′ indicatesthat for anchor duration greater than ΔX, the injector is operating in aspilt mode. The curve profile shown in FIG. 3 is representative ofaccumulated statistical data acquired from the performance test historyof similar injector types, with ΔY being a predetermined value derivedfrom the cumulative statistical average difference in fuel volumedelivered between boot and split modes.

The operating mode of an injector can be altered by adjusting theduration of the anchor delay current signal. This is known as trimmingthe engine. A desirable magnitude of adjustment duration, known as theanchor delay current signal offset, is a predetermined value derivedfrom the statistical maximum duration of the boot condition, asrepresented by ΔX in FIG. 3.

A flow chart 84, having a first segment 86 illustrated in FIG. 4a, showsthe sequential process of a preferred embodiment of the presentinvention for trimming an engine, i.e., for detecting the operating modeof a given injector and adjusting the mode as needed. As shown in box88, the predetermined ΔX and ΔY values are recorded into the memory ofthe ECM 56.

In the preferred embodiment, the engine is operating at a steady statespeed. In addition the engine is also desirably operating at a steadystate load. The ECM 56 then determines whether the engine speed and loadare operating in a steady state, as indicated by decision box 90. Thevalues of the various engine trim lookup maps relied upon by the ECM 56include a corresponding fixed rail pressure and main shot duration. Ifthe engine speed and load are not operating in a steady state, the railpressure and main shot duration will fluctuate, making the data in thelookup maps inaccurate. Therefore, if a steady state is not detected,the engine trim test is abandoned, as indicated by box 92.

When the engine speed and load are determined to be in the steady state,the average fuel volume requested by the governor (not shown) for aninjection event is established, as shown in box 94. It should be notedthat this is the volume of fuel desired to be delivered equally to allcylinders undergoing an injection event, as opposed to the volumedelivered to an individual cylinder.

The ECM 56 then selects a first cylinder for testing, as indicated inbox 96. As shown in box 98, the anchor delay current signal duration isthen increased by the anchor delay current signal offset duration ΔX.Referring back to FIG. 3, it is clear that if the tested injector wasoperating anywhere in a boot mode, i.e., anywhere along the boot modesegment 82′, under steady state conditions, an increase in the anchordelay current signal duration of ΔX will cause the injector to switch tooperating in a split mode, i.e., somewhere along the split mode segment80′. Accordingly, a notable reduction in fuel consumption will berealized. Conversely, if the tested injector was operating in a splitmode in the steady state, it will continue to operate in a split modewhen the anchor delay current signal duration is increased by ΔX.Accordingly, any change in fuel consumption will be negligible.

As seen in box 100, the new volume of fuel requested by the governorover several complete injection events is established and averaged. Thedifference between the steady state volume of fuel and the new volume offuel for one injection event is then computed, as shown in box 102. Thedifference may be between the steady state volume of fuel and a specificvolume of fuel for a specific injection event, or the volume of fuel forthe averaged fuel injection.

In decision box 104, the difference computed in box 102 is compared tothe predetermined ΔY volume. If the computed volume is greater than theΔY volume, the ECM 56 establishes that the injector being tested wasoperating in a boot mode under steady state conditions, as indicated inbox 106. Conversely, if the computed volume is less than the ΔY volume,the ECM 56 records that the injector was operating in a split mode understeady state conditions, as shown in box 108.

In the preferred embodiment, the ECM 56 determines whether all cylindershave been tested, as illustrated by decision box 112 of a second segment110 of the flow chart 84 shown in FIG. 4b. If untested cylinders remain,the ECM 56 selects the next cylinder for testing as indicated by box114, and returns to box 98 of FIG. 4a to begin testing the selectedcylinder as previously explained.

In the preferred embodiment, upon testing all cylinders, the ECM 56determines whether it is desirable for all of the injectors to operatein a desired, or pre-selected operating mode, such as a boot mode or asplit mode, as shown by decision box 116. If it is desirable to have allinjectors operate in a boot mode, the ECM 56 decreases the anchorcurrent signal duration for each injector associated with a cylinderfound to be operating in a split condition by a duration of ΔX, asindicated in box 118. Conversely, if it is preferable for the injectorsto operate in a split mode, the ECM 56 increases the anchor currentsignal duration for each injector associated with a cylinder found to beoperating in a boot condition by a duration of ΔX, as indicated in box120.

In an alternative embodiment, the anchor delay current signal 76 may beincrementally altered by a time value smaller than ΔX until a moreprecise value is determined for the anchor delay current signal durationthat will yield a change in the injector operating mode.

In a further alternative embodiment, the ECM 56 is designed to detectthe operating mode of an injector 14, and regulate it as desired, bymonitoring the actual engine speed instead of, or in conjunction withthe fuel requested by the governor. A change in the fuel quantityinjected by an injector 14 due to switching from a boot mode to a splitmode will cause a corresponding change in engine speed, which will bedetected by the ECM 56 of this embodiment. In one embodiment, the changein speed may be determined by sensing the instantaneous firing speed ofa cylinder. The ECM 56 will adjust the anchor delay current signal 76 asneeded to cause the injector 14 to operate in the desired mode.

In one embodiment, the trimming technique disclosed may be applied toany injection signal having two injection shots. For example, aninjection signal including a pilot and main injection, or a pilot andanchor injection, or a main and anchor injection.

Industrial Applicability

Utilization of an injection method and system in accordance with thepresent invention provides for better emission control during certainengine operating conditions as explained above. Although a particularinjection waveform for delivering multiple fuel injections may varydepending upon the particular engine operating conditions, the presentsystem is capable of determining the timing associated with the anchordelay current signal regardless of the type of electronically controlledfuel injectors being utilized, and regardless of the type of fuel beingutilized. In this regard, the appropriate fuel maps can be stored orotherwise programmed into the ECM 56 for use during any steady statecondition of the engine. These operational maps, tables and/ormathematical equations stored in the programmable memory of the ECM 56determine and control the various parameters associated with theappropriate multiple injection events to achieve desired emissionscontrol.

It is recognized that variations to the steps depicted in flowchart 84(FIGS. 4a and 4 b) could be made without departing from the spirit andscope of the present invention. In particular, steps could be added orsome steps could be eliminated. All such variations are intended to becovered by the present invention.

As is evident from the foregoing description, certain aspects of thepresent invention are not limited by the particular details of theexamples illustrated herein and it is therefore contemplated that othermodifications and applications, or equivalencies thereof, will occur tothose skilled in the art. It is accordingly intended that the claimsshall cover all such modifications and applications that do not departfrom the spirit and scope of the present inventions.

Other aspects, objects and advantages of the present invention can beobtained from a study of the drawings, the disclosure and the appendedclaims.

What is claimed is:
 1. A method for trimming an engine operating in asteady state so that a plurality of injectors contained therein operatein a pre-selected mode, the method comprising: determining that a speedand a load of the engine are operating in a steady state; selecting oneof the plurality of injectors; detecting an operating mode of theselected injector; recording the operating mode of the selectedinjector; sequentially repeating the above processes for each remainingunselected injector; comparing the recorded operating mode of theselected injector to the pre-selected operating mode to determine whichof the selected injectors is not operating in the pre-selected operatingmode; and changing the detected operating mode to the pre-selected modefor each of the selected injectors detected to be operating in otherthan the pre-selected operating mode.
 2. A method for trimming an enginein a steady state so that a plurality of injectors contained thereinoperate in a desired operating mode, the method comprising: determiningthat a speed of the engine is operating in a steady state; detecting anoperating mode of one of the plurality of injectors; comparing thedetected operating mode of the one of the plurality of injectors to thedesired operating mode to determine if the injector is operating in thedesired operating mode; and changing the detected operating mode to thedesired operating mode for the one of the plurality of injectors.
 3. Themethod, as set forth in claim 2, further comprising the step ofdetermining the engine is operating in a steady state load.
 4. Themethod, as set forth in claim 3, wherein the injector modes of operationinclude a split mode and a boot mode.
 5. The method, as set forth inclaim 4, wherein an electronic control module in electricalcommunication with the engine determines the pre-selected mode byreferring to lookup maps.
 6. The method, as set forth in claim 5,wherein each injector delivers fuel to a respective cylinder duringrepeated injection events.
 7. The method, as set forth in claim 4,wherein an anchor delay current signal occurs for a portion of eachinjection event.
 8. The method, as set forth in claim 7, wherein thestep of determining the operating mode of the selected injector includesthe steps of: establishing a statistical average difference in thevolume of fuel delivered between a boot mode and a split mode;establishing a anchor delay current signal offset; establishing a steadystate volume of fuel delivered by all of the injectors for an injectionevent; increasing the anchor delay current signal duration by thepredetermined anchor delay current signal offset to cause a new volumeof fuel to be delivered by the injectors; recording the new volume offuel delivered by the injectors; computing a difference between thesteady state fuel volume and the new fuel volume; and determiningwhether the difference between the steady state fuel volume and the newfuel volume is greater than the predetermined statistical averagedifference in the volume of fuel delivered between a boot mode and asplit mode.
 9. The method, as set forth in claim 8, wherein the step ofrecording the operating mode of the selected injector includes the stepof recording that the selected injector was operating in the boot modebefore increasing the duration of the anchor delay current signalduration if the difference between the steady state fuel volume and thenew fuel volume is greater than the predetermined statistical averagedifference in the volume of fuel delivered between a boot mode and asplit mode, and includes the step of recording that the selectedinjector was operating in the split mode before increasing the durationof the anchor delay current signal duration if the difference betweenthe steady state fuel volume and the new fuel volume is less than thepredetermined statistical average difference in the volume of fueldelivered between a boot mode and a split mode.
 10. The method, as setforth in claim 9, wherein the step for altering the operating mode of aselected injector includes the step of altering the duration of theanchor delay current signal by the predetermined anchor delay currentsignal offset.
 11. The method, as set forth in claim 2, furthercomprising the steps of: detecting an operating mode of each of theplurality of injectors; comparing the detected operating mode of each ofthe plurality of injectors to the desired operating mode to determinewhich of the injectors is not operating in the pre-selected operatingmode; and changing the detected operated mode to the desired operatingmode for each of the plurality of injectors detected to be operating inother than the desired operating mode.
 12. A method for trimming anengine having at least one injector controllable by an electroniccontrol signal, the engine having an engine speed and load, the methodcomprising: detecting an operating mode of each injector; modifying theelectronic control signal to each injector; and detecting an operatingmode of each injector generated by the modified electronic controlsignal, wherein the injector modes of operation include a split mode anda boot mode.
 13. The method, as set forth in claim 12, wherein thecharacteristics of the electronic control signal are determined inaccordance with lookup maps associated with the engine.
 14. The method,as set forth in claim 13, wherein each injector delivers fuel to arespective cylinder during repeated injection events.
 15. The method, asset forth in claim 14, wherein the electronic control signal includes ananchor delay current signal for a portion of each injection event.
 16. Amethod for trimming at least one fuel injection device associated withan engine, the injection device injecting multiple fuel shots inaccordance with an electronic control signal generated by the engineduring a fuel injection event, the method comprising the steps of:sensing a first engine speed; modifying the electronic control signal;sensing a second engine speed; and determining an operating mode of theat least one fuel injection device in response to said first and secondengine speeds.
 17. A method, as set forth in claim 16, wherein theoperating modes include a split mode and a boot mode.
 18. The method, asset forth in claim 17, wherein each injection device delivers fuel to arespective cylinder during repeated injection events, the injectionevent including a first injection and a second injection and aninjection delay between the first and second injections.
 19. The method,as set forth in claim 18 wherein the step of modifying the electroniccontrol signal further comprises the step of modifying the injectiondelay.
 20. The method, as set forth in claim 18, wherein the step ofmodifying the electronic control signal further comprises the step ofincreasing the injection delay by a predetermined amount.
 21. Themethod, as set forth in claim 18, wherein the step of determining theoperating mode of said first and second engine speeds further comprisesthe steps of determining a difference between said first and secondengine speeds; and determining the operating mode is a split injectionmode when said difference is less than a predetermined threshold. 22.The method, as set forth in claim 18, wherein the step of determiningthe operating mode of said first and second engine speeds furthercomprises the steps of determining a difference between said first andsecond engine speeds; and determining the operating mode is a bootinjection mode when said difference is greater than a predeterminedthreshold.